Flame detector system



Sept. 8, 1959 J. F. VAN DRIEI.

FLAME DETECTOR SYSTEM Filed Dec. 28, 1955 SSS was owl@ WEEE I., INVENTOR 2,903,682 FLAME DETECTOR SYSTEM John F.1Van Driel, Irvington, NJ., assignor to Pe-tcar Research Corporation, Washington, D.C., a corporation of New Jersey ApplicationDecemberZS, 1955, Serial No. 555,932

1 Claim. (Cl. 340-227) This invention relates, in general, to fire detector systems and, more particularly, to such systems which are operative to provide a'signal only when actual Vflame mpin-ges on the sensing element of the system and ground.

Systems of the` particulartype to which the invention relates are known and it has been the principal object of the invention to provide a simplified system of this type which is constructed and operative in a new and improved manner to provide an indication of fire only upon impingement of actual flame on the sensing elementv and-ground. A further object of this invention has been to provide a fire detector system which will produce a signal when a iiarne impinges on the sensing element yand ground but which will not be operative by irregular intermittent pulses such as rain and the like. Other objects and features of`novelty of the invention will be made apparent by the following description and the annexed drawing, in which:

Fig. 1 is a blockv diagram of a fire detector system according to the invention in which the sensing element is' connected to a source of direct current, and

r 2,903,682 Patented Sept. 8, 1959 Ice " frequencies, a voltage will be produced between the sensing element and ground that will have the same frequency as the frequency of the flicker of the flame. The voltages so produced are amplified and supplied to an amplitude discriminator circuit which produces a voltage pulse when the amplified output exceeds a predetermined level, thus eliminating the effect of inherent circuit noise within the system, hum and other such extraneous noises. An integrating circuit is connected to the output of the discrirninator circuit to integrate the discriminator output. The integrator causes the detector system to be responsive only to signals having a definite minimum duration and to not respond to signals of a shorter duration such as those that might be caused by rain, static electricity discharges and other similar signal sources. The output of the integrator is amplified andsupplied to a relay` which device.

A` flame detector system according to the invention is shown in block diagram in Fig. l and comprises a sensing operates v an indicating v element or electrode 2 which may be any bare electrode the voltage source.

Fig. 2 is-a block diagram of a re detector system--V according to the invention in which the sensingelement is connected to a source of alternating current.

It has heretofore been observed (see Industrial and Engineering Chemistry, vol. 20, No. l0, page 1012, October, 1928) that the upper portion of the luminous zone of a flame rises to a maximum height at a regular frequency which m-ay be between three and thirty times per second but which is most prevalently ten times per second, and that the lower portion of the luminous zone of the ame has a continuous existence but periodically, at the same frequency as the upper part, gives olf another ame which rises above the lower portion of the liame during its short period o-f existence. It has been found that the rate of this flickering of any flame is not greatly affected by change in conditions to which the flame is subject and will remain fairly constant within the limits set forth above. In the present invention I have utilized this characteristic of a flame to iiicker at -a frequency within well-defined limits to provide a system which produces an indication whenever a flame impinges on the sensing element forming part of the detector system.

According to the invention a bare sensing element, which is insulated from ground, is connected to a source of direct or alternating current. Impingement of a flame upon the sensing element causes current to flow between the sensing element and ground. The magnitude of the current is determined by the size of the flame and by the degree of contact between the flame and the sensing element and between the flame and ground. Due to the flicker of the flame none of these quantities remains constant. Therefore, the magnitude of the current will vary at the same frequency as the fiicker of the ame. If the voltage source presents a reasonably high impedance to the ow of current at these such as a wire, screen or the like, and which is insulated from ground by insulators 4. A source of direct current 6 is connected between ground at 8 and the input end of electrode 2 through a band reject filter 24. The -band reject filter serves the dual purpose of insuring that the voltage source presents a high impedance to the sign-al produced by the ame and of preventing any possibility of operation of the detector by signals from anyv other source which might be transmitted through Normally, no current flows in the electrode 2 as it is not grounded, but when a flame impinges on it a current will flow because of the grounding of the ame and this current will pulsate at the frequency of fiicker of the fiame.

Voltage pulses produced in the electrode must be amplified to provide sufficient power to actuate a signal device. The fluctuating voltage produced in the sensing element upon impingement of a flame on both the element and ground is accordingly supplied to a band pass amplifier 10, through a band pass filter 26, both of which are responsive to sign-als in the 3 to 30 c.p.s. range. The band pass filter, 26, is so constructed that it will pass frequencies in the 3 to 30 c.p.s. range and will reject but not short out all other frequencies. To reduce the possibility of hum and circuit noise producing a signal, an amplitude discriminator 12 is connected to the output ofthe amplifier 10. This amplitude `discrirninator may be a circuit known as a Schmitt Trigger circuit which may be made to operate so that when an A.C. signal that is above a certain adjustable minimum is applied to the input, the output is essentially a square wave of the same frequency as the input. The minimum is adjusted so that circuit noise, hum and other similar noises produced in ythe detector will not produce an output but the signals produced by a flame impinging on the sensing element and ground will produce an output. Thus the effects of inherent circuit noise and low-level spurious voltages are minimized.

The output waveform from the amplitude discriminator is supplied to an integrator 14 which has circuitry such that it will not produce an output of suliicient amplitude to cause operation of the relay circuit unless its input signal is of a certain minimum duration. This produces a delay in operation of the relay circuit such that large sporadic signals such as those produced by rain, static electricity discharges and the like will not cause operation of the relay circuit. The delay is, however, short enough for the reaction of the detector to liame to be considered instantaneous. In this manner the effect of low frequency spurious responses are minimized.

3 The combination of the Schmitt trigger and integrator circuits produces a voltage which is essentially li11- dependant of the amplitude and frequency of the signal into the Schmitt trigger. The trigger circuit produces a constant amplitude square wave whose frequencyis the same as thefrequency at its input. When this square wave is integrated by the integrator, its output is eS- sentially. the same for any frequency.

The output of the integrator is coupled to a relay control tubel which operates a relay 18. As the voltage output of the integrator' is a relatively slowly rising voltage whose: amplitude is determined by the duration of the signal to it, the relay is adjusted to operate at a pre-determined .voltage which is above that caused vby; spurious signals andbelow that caused by flame. Operation of the relayconnects an indicating device 20, such as a lamp, toy a source of electrical energy 22 to energize the indicating device.

In the operation of the detector system according to this invention a low voltage direct current is constantly available at the sens-ing element 2 but normally does not flow therein because of the insulation of the sensing element from ground. When a fiame impinges on the sensing element and .ground the pulsating or flickering character of the flame distorts the direct current voltage between the sensing element and ground causing pulses to be produced at the frequency of the flicker of the flame.` These pulses are amplified and passed to an amplitude discriminator if their frequency lies Within, the 3` to 30 cr.p.s. band pass width of the amplifier. The amplitude discriminator eliminates all pulses below a predetermined voltage and supplies those of greater volt-1 age to an integrator which eliminates all signals not having a minimum. duration and which are of a frequency. lying within the aforesaid range, thus eliminating signals due to extraneous causes `such as rain. The output of the integrator is supplied to a relay control tube which operates a relay when energized, to cause operating. ofl an indicator, thus indicating the impingernent of flame on the sensing. element and ground.

In Fig. 2 of the drawing there is disclosed another embodiment of the invention in whichy the sensing ele- 4 pass filter 48 to'a band pass amplifier 32, the output of which is connected through. amplitude.discrimiuator3, integrator 36 and relay control circuit 38 to relay 40 which controls the connectionl of indicator 42 to a source of electric energy 44. In all respects, the operation of the system disclosed in Fig. 2 is the same as that of the system disclosed in Fig. l. Normally, no current flows from the sensing element 2 to: ground but when a grounded llame impinges on this element` `an alternating current will fiowlbetween the wire and ground atthe frequency offiicker of the flame. The distorted alternatingw current will'appear at the input to the' band pass filter 48 which will pass only the frequencies of flicker for the band-.passramplifier 32. to. amplify, and willreject but not short out all other frequencies. .The function and operation of the partsof' the system following amplifier 32 are exactly the same as described hereinbefore in connection with the system.I disclosed in Fig. 1 and no fura ther descriptionwthereof is belieyedtoy be required.

.'While I; have, described f and illustrated certain forms which'gmy invention may take it.` will beapparent tothose skilled in. the art thatotherfembodiments, as well as modifications of those disclosed, may be made and practised' without departing inA any way frointhe spiritI or '30 gwunia; source: ofelectrie energy connected between.

sQQpepeof the invention,v for they limits ofv which reference; must be made; tothe appended claimt;A

What.-is claimed Yis:v

A ame detectorgsystern comprising-a sensing. elesaidelectrjode and ground., means forr amplifying .voltage pulsestproduced .betweenv said lelectrode' and ground by imp ingement-o-f a flamesimuItaneQuSIy-on. said elec-.,

3 trode.- and ground, ,amplitude discriminating, means admitting amplified .signal voltages. appearing between said electrode and ground exceeding..apre-determined. amplitude and rejecting other amplifiedgnoise vvoltages belowsuch'pre-determined amplitude,.means; for in tegratinggthe;y squarewave output of*` the amplitude discriminament 2 is connected to a source of alternating voltage,

3@ through a band reject filter 46 instead of the source of direct current 6 of the embodiment disclosed in Fig. 1. The band reject filter, as before, will present a high impedance to the signal produced by flame and will prevent operation by signals from the source. The fre quency of this source is such that it will not be in the 3 to 30 c.p.s. range and one to which the band pass amplifier will not respond. The sensing element is insulated, from groundby insulators 4 and therefore no current normally flows in the element. The output end` of the sensing element is connected through a band tor over a unit of time, indicating means, Vand means for operating-the indicating means when the outputof the integrator reaches a, pre-determined. voltage.

References Citedin .the le of this patent UNITED STATES PAT ENTSV 2,385,976.. Evans` Oct.v 2, 1945 2,455,350 Beam Dec.l 7, 1948 2,564,596, Dahline Aug. 14, 19.51 2,697,824. Norton Dec. 21, 1954 2,722,677` Krueger Nov. l, 1955 2,730,304 Markow Jan. 10, 1956 2,820,945 Marsden Jan. 2l, 1958 

